How to change themes or delete content?

I selected a theme and I no longer think it will work, but I am unable to change it. I tried to delete content, but I was instructed to ask for help. I would like to know how to start over, or better yet, how I can change my theme.
Blog url: http://librarianreviewspopscibooks.wordpress.com/

Annotum is a theme for the Google Knol people who migrated here. I have flagged this thread for Staff attention as you can't seem to switch themes here > Appearance > Themes select a theme - click activate.